There already exists a technique making it possible to determine the internal diameter and external diameter of a transparent tube. A technique whereby the external diameter of the tube is determined by means of a first measuring device and the thickness of said tube is determined by means of a second measuring device distinct from the first device, a knowledge of this thickness then makes it possible to determine the internal diameter of the tube.
This known technique using two devices is an expensive technique.
There also exists another technique making it possible to determine the internal diameter and external diameter of a transparent tube, this technique being implemented in a device sold by the YORK TECHNOLOGY company under the reference P101. According to this other technique, the internal diameter and external diameter of the tube are determined by means of optical index measurements and the tube needs to be placed in an index attachment liquid.
This other known technique is totally unsuited for the "continuous" measurement of the geometrical characteristics of an tube being produced which needs to run off in front of said device.